Electronic equipment packaging



April 19, 1960 GRADISAR ETAL 2,933,655

ELECTRONIC EQUIPMENT PACKAGING 3 Sheets-Sheet 1 Filed Jan. 31, 1957 INVENTOM ALBIN A. GRADISAR ALFRED S. GUTMAN JOHN A. MEYER ATTORNEY April 19, 1960 GRADlSAR ETAL 2,933,655

ELECTRONIC EQUIPMENT PACKAGING Filed Jan. 31, 1957 5 Sheets-Sheet 2 INVENTORS. ALBIN AGRADISAR ALFRED S. GUTMAN BY JOHN A. MEYER ATTORNEY.

April 1960 A. A. GRADISAR E'rm. 2,933,655

ELECTRONIC EQUIPMENT PACKAGING Filed Jan. 31, 1957 i 3 Sheets-Sheet 3 [F 7 9O 88 G 8 Low Temperature 0 r i Ambient (Mg. 50 F) 76 44 !41444444 H1: 5 1 92 COMPONENTS WITH LOW '00 HEAT DENSITY f I/ I l/ I I/ z I/ I 1 ll 1/ 1 If 11 1 98 Exhaust Air (e.q.,250F) Source of cooling air coohng cur [F IG. 9 \HO uo COMPONENTS 6 n2 COMPONENTS o WITH LOW wmr LOW I HEAT DENSITY 76 Medium \76 Temperature 06 Ambient [06 (0.9.,260 F) High Temperature Ambient (e.g.,800F'} Exhws' l 2 Exhaust Air (0435 1") gsoflr 9B INVENTORSY ALBIN A.GRADISAR ALFRED S. GUTMAN BY JOHN A.MEYER AT TOR N EY 2,933,655 ELECTRONIC EQUIPMENT PACKAGING Albin A. Gradisar, Los Altos, Calif., Alfred S. Gutman, Auburndale, Mass., and John A. Meyer, Tonawanda,. N.Y., assignors, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Application January '31, 1957, Serial No. 637,476

11 Claims. (Cl. 317-100) This invention relates to heat transfer apparatus, and is more particularly concerned with a packaging and cool-, ing system for electronic equipment operating in an elevated temperature environment and where economy of cooling fluid is of extreme importance. Most of the electric power used to operate present-day electronic equipment is converted into unwanted heat;

components of the chassis that adequate cooling is provided by natural convection of air over the assembly. In certain specialized electronic equipment, however, where space and weight are of prime importance, miniaturization is employed, resulting in much greater heat density and the attendant requirement of transferring the heat from the chassis. A good example is in the case of airborne electronic equipment where obviously economy of space and weight is very important. Electronic equipment for installation in subsonic aircraft has been designed with little emphasis on cooling, the equipment simply rejecting its heat to the surrounding air and to surrounding structure, depending on free convection, or

in some cases, the cooling air being circulated at low velocities by small blowers. In most applications, this .method of cooling was satisfactory since the ambient air temperature was low relative to the operating temperatures of the equipment, or a source of cool air could be made available through utilization of the blower. With .the advent of supersonic aircraft, however, new problems are presented since under critical conditions, the resultant ram air temperatures exceed the allowable operating temperatures of some electronic components so that the use of ram air for cooling becomes impossible unless its temperature is lowered. Therefore, some otherheat sink must be used and if air is to be utilized as the cooling medium, a refrigeration system is required. This results in a performance penalty to the aircraft by reason of the weight of the refrigeration system, andbecause power.

is required to operate the refrigeration system, which increases the fuel consumption. Consequently,it-is desirable to provide electronic equipment cooling with the minimum flow of cooling air in order to minimize the resultant range penalty.

If the electronic equipment heat load in the cabin of the aircraft is simply rejected to the surrounding cabin air, as was the practice in the past, the cooling load in the cabin conditioning system will be increased by exactly that amount. However, if the equipment is thermally insulated from the cabin and is designed to be cooled by exhaust cabin air, just before the air is to be dumped overboard, no extra load is imposed on the air conditioning system, provided the amount of air required for te r1Arr...19.1960

electronic equipment which has a fixed heat rejection, it

is obvious that the cooling air flow required can be 7 minimized by either decreasing the cooling air temperature at the inlet to the equipment or increasing the exit air temperature. The inlet air temperature is a function of the characteristics and design of the -aircraft refrigeration system and supplies air at a temperature as low as is compatible with other airplane considerations. If the exit temperature can be increased while holding the inlet temperature constant, a smaller volume of air is required to remove the fixed heat load, andif this increase in the component surface temperatures, that is, if the components'can be maintained at a temperature at which they are reliable in operation, improved cooling efficiency will have been achieved.

The major part of the heat dissipation from electronic equipment is generated by the vacuum tubes, and efiicient cooling of any electronic package requires that they be efliciently cooled. Also, since vacuum tubes normally have higher allowable surface temperatures than the rest of the components, efiicient cooling of tubes will permit a higher exit air temperature from the package, thus accomplishing the objectives mentioned above. One approach which has been employed to improve cooling efiiciency is the so-called cold-plate technique, which uti- 'lized a double-walled metallic container for the electronic package, with the cooling air directed through the double wall. The tubes are enclosed in tightly fitting shields, which, in turn, are clamped to the colder wall of the container. Heat is transferred from the tubes to the shields and thence to the cold plate by conduction, and from the cold wall to the cooling air by convection. With careful design, the cold wall package does not appreciably add to the weight of the equipment, but the systemhas certain inherent inefficiencies. It is generally agreed that for reliable operation of most sub-miniature electron tubes, the average temperature of the envelope must be kept below 280 F. It has been found that to accomplish this, theshield enclosing the tube must be kept to about 270 F., and the cold plate kept to about220 F., with the consequence that the maximum temperature at which the cooling air can be discharged is about 180 F. This increase in exit temperature results in someimprovement in the efiiciency of utilization of avilable coolant but the spread of 100 degrees between the exit temperature and the temperature to which the tube must be maintained indicates that further improvement is possible. That is, if the exit temperature could be made more nearly equal to tube temperatures at which reliability considerations are satisfied, then a lower volume of cooling fluid would be required.

Another aspect of the problem is the conflict between electronic design requirements and the cooling requirements of the package. In general, the electronic designer prefers to arrange components in a functional manner and, of course, it is often necessary to give special attention to the length and placement of leads to prevent pickup or interference. It will be apparent that a location of components to satisfy electronic requirements may be inconsistent with a location where the heat generating components can be efiiciently cooled components of the assembly.

by the cold plate or'other cooling arrangement. In

general, the electronic designer is'not permitted significant latitude in the arrangement of parts, and, accord ingly, it is desirablethat a cooling .systembeprovided which-will allow, independent cooling of the hot compo- ,mentswithout sacrificing efficiency in the utilization'oi-the cooling medium. Moreover, the system mustbe practi- -'cal, and not materially increase theweight or volume of j the electronic package.

With an appreciation of the shortcomingsv of available cooling systems andthe problems attendant the ccoiing .of specializedelectronic equipment, applicants have as a primary object of their invention to provide a cooling system for .electronicequipment operating in anatural environment which is. hotter .than. the vhottest individual ..-.Antheri object of the invention is to provide accoling system. for electronic equipment which willvmake a maximumuse. of cooling fluidof limited availability.

,Another objectof the invention is. to. provide a'systern for packaging equipment .wherein. .the. conflict be 1:.-tween,.-;electronic.qdesign considerations and. thermody- ...-;.namic .designconsiderations. are essentially resolved.

..Another objectof the invention isto provide acoolring system for electronicequipment.which.does, notma- ....,terially add to the weight or volume. of the equipment.

- vThese and other objects which will be apparent as -the description proceeds,-are achieved by the present invention by a combination of techniques includingisolation of the'hotter components-from the lower tempera- .ture components both bydistance and thermal insulation, insulation of. the high heat density components, the low heat density components, or both, from the surrounding ambient, and passingthe cooling '"air directly in contact with the hot components, the passages for airflow being designed to provide a sufficiently high heat transfer co- ...efficient that the exitair temperature is not materially In a preferred vembodimentotthe .invention 'which-areusually. of thesubminiature type. in equipment wiof.-.the type here .under discussion, aremounted; on an wedge; of the 'circuit:board.and: extendtherefrom inthe Hplane of the board. .Thetubes', initurn, arev surrounded r-z'by conductive.:electrostatic shields provided with means for spacingthe shields .a predetermined distance from. the tube envelope to provide an annular passage of conitrolled dimensions for thecooling air. *;.shields are surrounded by' thermal insulation, such as plight-Weight foamed plastic, which insulates the tubes from the other components of the circuit and from the :;:ambient. .An air duct is formed in the foamed plastic 'for receiving theair after passing'over the tubes and to "discharge it into an external reservoir. Coolingair is f drawn into the system and passes over the components in the direction of ascending temperature; that is, the

' inlet air first passes over the capacitors and resistors,

.1 which normally must be operated at relatively low. temperatures to insure reliability, then over the exposed leads of the vacuum tubes, which have a lower permissible temperature than other parts of the tube, through the annular space between the tube and shield, and into the duct and exhausted. In this connection, it has been determined that certain areas-of thetube may be operated at higher temperatures than other areas and that conse- -"quently it is unnecessary to keep theentire tube at the lowest permissible temperature in order to have reliable operation of the tube. For example, it has been found that at thehot spot on the surface of the-tube,

which is usually in the region of the anode, reliable"op The tubes and eration is obtainable even if the temperature goes as high as 330 F.,whereas a temperature of the orderof'300" F. in the vicinity of the tube leads may cause tube failure. Consequently, the cooling air is directed to reach the tube leads first so as to cool them to the lower temperature necessary for reliability, the resulting increase in temperature of the air, however, notbeing so great that the hot spot cannot be cooled to a safe temperature. In a chassis which includes a plurality of tubes, as is usually the .case, the air is introduced tothe tubes in parallel, the

volume of the air flowing over each of the tubes being adjusted, for any predetermined exhaust pressure, in accordance with the heat dissipation of the individual tubes, to provide an optimum compromise between the maintenance of all areas of the tube at a temperature where reliable operation results and an exit air temperature as high as possible. The distribution of cooling air is accomplished bymetering orifices and contributes to the overall efficiency of the cooling system, inasmuch as only that .coolanttov maintain. the tube at a reliableoperating temperature issupplied. tov eachetube, thereby. reducing the overall expenditure oicooling. air. I Inanothenembodiment of. the invention, the electronic assembly is more or. less. conventional in that the. tubes .are mounted perpendicularly to a flatcircurt board. on

one side thereof, with resistors, capacitors, etc.,- mounted on the other side; Tubesockets are not used, however, the tube simply being supported on its leads which extend through openings in the board and are connected to the resistors and" capacitors. Each module is provided with its own plug-in connector, maintenance of the system being accomplished by replacement of modules. Consequently, fewer connectors are needed than there are tubes, and the connectors being spaced from the tubes and operated at lower temperature, improved reliability is achieved. As in the above-described embodiment, each tube is surrounded with a shieldwhich formsan' annular passage .for. airaround the. tube,. and the shield s. sun

rounded by thermal: insulation having a duet .t'orrned thereirrfor'i exhausting. the coolant. .In this arrangement,

' the coolingair is" first drawn over resistors; capacitors,

etc., then flowsxthrough. the openings in the board over .thetube: leads, through the annular. space betweenihe tubeand' tube-shield, and thence through a metering orifive into the exhaust duct.

Other .objects,zfeatures. and advantages ofzthetrinvention, and a better understanding of its: construction." and operation will 'be apparent from the following detailed description taken in'connection with the accompanying drawings in which:

Fig. l is a perspective view, partially cut away, of an electronic'chassis embodying the principles of the invention;

Fig. 2 is a schematic representation of a printedcircuit board of the type employed in the chassis of Fig. 1;

"Fig. 3- is a perspective view illustrating the mounting sub-miniature tubes on the edge of a circuit board'of the type illustrated in Fig. 2; r

Fig. 4 is a fragmentary cross-sectional view of a portion of Fig. 1 illustrating the details of the tube mounting and tube shilde;

ciples of the invention;

Fig. 7 is a fragmentary cross-sectional view'of a portion of Fig. 6 showing the details of the tubemounting and its shield; and

; Figs. 8, 9 and 10 are schematic diagrams illustrating the application of the invention to different ambientconditions.

4 Referring to the drawings, and more particularly to Fig. 1; the cooling techniques" in'accordance with" this plastic.

* to exhaust coupling 32.

1" invention are particularly applicable to electronic equipment made up of a series of modules or sub-components,

a type of construction currently used widely in the assembly of airborne electronic equipment. In the illustrated arrangement, the supporting structure for the chassis consists generally of a rectangular box having a metallic outer shell preferably formed of light-weight material, such as aluminum, having a cover 12 formed of insulating material such as glass cloth laminated The chassis is made of a plurality of subcomponents or modules, each mounted on a circuit board (to be described in more detail in connection with Figs. 2, 3 and 4), vertically positioned above the container 10. The lower edge of the each of the terminal boards 14 rests on the cover 12 with the tubes 18 of the sub-chassis depending therefrom and passing through openings 16 in "the cover 12.

A tube shield 20 surrounds each of' the tubes, to provide electrostatic shielding and to form an annular passage for cooling air around the tube. The

lower end of each tube shield rests on an orifice plate- 22 which has an opening 24 therein for controllingthe volume of air passing over each tube. The orifice plates 22 are supported on plate 26, spaced from and parallel to cover 12, plate 26 with plate 28 forming an exhaust duct extending across the width of the box 10. Atthe right end of the duct, as viewed in Fig. l, the duct narrows into a manifold 30, which, in turn, is connected The spaces between cover 12 and plate 26, and between plate 28 and the bottom plate of container 10, are filled with a light-weight thermal insulation 34, such as foamed plastic, which serves to thermally insulate the tubes to prevent the heat dissipated thereby from affecting'the rest of the equipment.

Each of th ecircuit boards 14 is supported in a frame 36 preferably formed of thin, light-weight sheet metal with upstanding ends 38 and 40, which may be secured to cover plate 12 as by screws 42, and a top portion having a rectangular aperture 46 therein. An electrostatic shield 48, essentially a rectangular open-bottomed box, also formed of light-Weight sheet metal, is provided for each sub-chassis, fitting over the support 36. Each of the shields has a rectangular aperture 50 therein, located to be in register with the aperture 46 in the support 36 when the shield is in place, to permit the'entrance of cooling air and distribution along both sides of the board From the description thus far, it will be seen that the tubes of the chassis are thermally insulated from the ambient in which the equipment is placed, and from each other, and from the other parts of the chassis which are normally operated at a lower temperature than the tubes. With the tubes thus insulated, it is obvious that there can be no cooling of them by natural convection, and accordingly, air must be passed over them to remove the heat which they dissipate. In the disclosed arrangement, ambient temperature air (if the equipment is located in a conditioned cabin), or air from an air conditioning system (if the equipment is located outside a conditioned cabin), is drawn through the aperture 50 of the electrostatic shield 48 and passes over both sides of the circuit board 14 to first cool the resistors and capacitors of the circuit which are assembled thereon. After passing the circuit board, with some increase in temperature, the air passes over the leads of the tubes 18, the leads being exposed on either side of the board 14, and enters the annular space between the tube envelope and the tube shield. It is generally recognized that the tube in the vicinity of the leads must be kept cooler than other parts of the tubes for reliable operation, since electrolysisin the glass is most likely to occur in this area at elevated temperatures. By cooling the tube leads and the base prior to the other parts of the tube these sensitive areas are kept the coolest. In passover the tubes, the air temperature is further in- -=-creased,- there being a substantial gradient-from the base to the top of the tube, the openings 24 in the orifice plates 22 being designed to provide a flow of air-therethrough to provide a maximum exhaust temperature consistent with cooling of the tube to a temperature to insure the desired reliability. As an example, in a system embodying the invention, it is possible to exhaust the cooling air from the electronic package at a temperature of 250 F. while maintaining the temperature of the tube sufiiciently low for reliability, say 330"" F. at the hot spot of the tube. The heated air from all of the tubes of the chassis enters the duct formed by plates 26 and 28 and is exhausted through coupling 32 into a reservoir'separate from the equipment, preferably overboard in the case of an aircraft. The exhaust equipment for removing the heated air from the package forms no part of the present invention, and consequently has not been illustrated, but in general, must possess the properties of providing a pressure differential between the inlet aperture 50 and the exhaust manifold 30 to draw cooling air through the system with sufiicient velocity to provide a satisfactorily high heat transfer coefficient. It will be noted that the tubes are cooled in. parallel; that is, the supply of air entering openings 50after passing circuit board 14 is presented to all of the tubes (in that module), the distribution of the air therethrough being determined by the sizes of the orifices associated with the several tubes. Thus, any tube can be mounted on the board in a position compatible with favorable electronic design, yet can be satisfactorily cooled by proper design of the orifice. Parallel flow also permits selection of orifice sizes to regulate the amount of air flowing over the tubes in accordance with their heat dissipation, so as to expend only that quantity of air necessary to maintain the tube at a safe temperature. With some tubes it may be possible to exhaust the air at a higher temperature than with others, or adequate cooling may be possible with less air flow, thus permitting considerable flexibility in the placement of parts while affording adequate cooling. While the system has been described as having only tubes extending fromthe circuit board and thermally insulated from the rest of the circuit, other dissipative components capable of operating at elevated temperatures, for example certain types of resistors and possibly transformers, may be similarly mounted and subjected to the preferential cooling afforded by the parallel flow system. 1'

As was noted earlier, much of the heat dissipated by vacuum tubes is transferred by conduction by the metallic leads of the tube, and accordingly to remove the heat from the system, means must be provided efficiently to transfer this heat to the coolant. In accordance with this invention, tube sockets of the conventional type, which would prevent flow of air in direct contact with the tube leads, are eliminated, baseless tubes 18 instead being employed and mounted on an edge of the circuit board 14 as shown in detail in Figs. 2, 3 and 4. As best seen in Figs. 2 and 3, one edge of the circuit board14 is provided with a series of projections or tabs 1411 at the points where the tubes are to be located. The tube is. joined to the tab 14a. by a two-piece retainer, formed of insulating material such as Teflon, consisting of a ring and a serrated plug 62 having a diametral slot I 64 formed therein for receiving the tab 14a. Since most tube are placed in the grooves of plug 62 as shown, the ring 60 placed over the plug to retain the leads in the.

grooves, this assembly then beingafl'ixed to the circuit,

212;933355 A, 7 8 esboard by inserting: tab= 14a; intonslot 64eutithithe' :tube zmssemblymay -belightei: in-zweightithau therconventional qleads 'dlSiZIiblltEditOi opposite i'sidesmf theaboard. With :gassernbly. ';F1'0m ihegstandpgintof volume, titheaspace a the leads soldered toi'terminals or".other;:.circuit-. com- .::around,1he tubes; inconventional packages is normally Pollents .011 Ihe hoafdtlli, fl Ielatilfily g Y- :open; to permit cooling by natural convection, but-nonethe 13h '14l11aI1d the Wiahlfif; Sen/h1giO p i n. iiitheless contributes. toithe overall volume of the package; "..the' tube in t e P -Of t fl It Will-he $661- that :thus', theplacement of the foamed plastic around the tubes this construction exposes the;leads;of the tube whereby i th present system e ll d t t ibut to th air flowing over .the sides;of. the board'may pass in ll v l f h k direct contact. with:the: leads as it flows: towardtthe W fl h d i f h tubes, on the (;i1'c 11it tube envelope- 10 board affords optimum cooling of the tube leads as aboveflowing hvel'fahd' s the leads, thfi is .:..described', the-*advantagesiof: thei'invention may :also-be constrain d t how 6 vihfi tube envelope 18, by "realized by positioningtheptubesperpendicular to a1ciri I filhe Shield-29, which Surrounds the tuhefihd is embedded cuitboard on one isidev thereof, and. arranging thejother in thfi foamed In the fabrication of packircuit components such a resistors and capacitors on .1 age, ..the tube. shields are positioned between plate 1 26: thepther Side f the board as Shown i i 6 d 7,; .1 lilal'ld'the' cover-12; ih-register'whh the opemngs in'ihe Fig. 6, the invention. is illustratedv as embodied; in a 1, cover; andwith the orifice plate 22 in place, the volume Single Subchassis module, instead of man integrated :xbetween' theplates. isfilled with foamed plastic, such: as System15 was the case. in Fig 1' i baringv understood =::,;polyisocyanate, a two-component toam-in-place plastic however; that a group of assemblies f Fig 6 may :,..material,..which is. non-,toxic, will withstand normal oper-s, placed side,by=side farm larger wassmnbh, tithe iii-atioh-tempemtures-nfi 390-0 -'f j SPPPOM situation requires. sln thiszcase, .the foamed'plastic, libeustlonji foamed P135tlcv i hght fi havmg whichmawbe polyisocyanateaas, in..the previously. dea:dens1ty.as low as.3: to 41.pounds.per.cubrc. foot, wh ascribed :system; is cast into arectangularshaped; block t. sufficient; arr. 1S.11'1t1OdllC(l,;yiZ .fOImS a. strong, Ilgld, andfitted with metallic capsrniandlm whereby self-supporhm;structure;.Unlikei conventional; tube....2 5 japchassisrboardlm (to besdescribed in more detail). mav ::.shields, the shield 20 is-provided with .a longitudinal. slit nbelsecured thereto asiby Screw vAn air duct is fcrmea .20agextend1ng: from the. lower. end over; most of .the in; the block near edge thereof, substantially COLE length. of the shield whichterrninates in a cut Ztic extend- ,tensive with the block, and may constructed of a i around most the Penphery i shleld t tube 78 formed of laminated plastic insulating material fi to radla? expansion of In having a rectangular crosssection and closed at one end :addrtron, a plurality of dimples 2012 are formed 1n the J and open. at theothen end for the exhaust of am A :wall of theshield for example at two locations along 1 m series of cylindrical opemngs 79, the number depending :Itne kmgth thereof with three dlmples equally Spaced upon the number of tubes in the chassis to be cooled, are

1 d the Shield at g urpcse formed in the block 70 and extend across the block and If the i g g i gi i i g 0 in communicate with theduct 78 through orifices 80 (Fig. 7) f inven't'idn g found that a are between't'he t r several orrficesare'designed' so that for any predeter- Ii Shiela g y maintain a Satis mined chamber exhaust pressure, each tube receives .rfactory temperature. gradient along the tube, but inas 4 ggzi figg g g g ig g i ig a Chalkboard 1 much as the manufacturing tolerance on the diameter of i76rwhich maybe formed of laminated p1 astic with the sub-miniature tubes is in excessof ,O30", it is impossible 84 and Shialds 86 therefor mounted one Sidg to. aint 'n th's s acin without thecustorn manuacture e of gshii ldfc irgach tube a practice which obiIiousl-y "perpendicular the f and the remammg 01min could not be tolerated where mass production is. indicated. 332 335 5: figii gi gi s x 2: i gfj fig The provision of dimples 2%, which extend radially in- 7 h b M 86 2 ward from the wall of the. shield 'by..030, and together t e m S Sum .constmcnon 9 t at with the sprin actiouafiorded by slot 26a and cut 200 '1Hu.strated.m having a longitudmal Slot and i ainsures that thetube envelope is always spaced .030 Instead o.fibe.mg cast Into the fo.amed plastlc from. the shield in spite of variations, in the diameter 2 22 d 9 f g g ifi i 2 g z i part of the tube. Apart from the heat transfer requirements, 2 e o r may be copper-clad as lndicated at 92, and one end of the the shield also serves rigidly to position the tube. to

I n shleld 86 provided with'a flange 86d, 15 soldered thereto. any Whlch mlght'b'e plmd the The-tube s4 is fitted within the shield, the tubeleads aft gigg i g igi gg 1e ds to the 01mm board 14 53 passing through an openmg94 1n crrcult board 76and At the base of e'ach Shield is a thin plate 2a havin joined to the other circuit" components and/or terminals g p 1 sharp-edge metering orifice'24 therein to proportion the gg'i g 5; i i ig f shheld amount of air for each tube in accordance with its power L 0 e Oar er W1 1 grin: c ampmg .dissipation. From the system standpoint the orifice di- Y acuon between the shlleq and tube mlfnlmlzes Sitram on ameters of the Several tubes are so designed that b the tubeleads, and provides amechanrcally satisfactory 'tany predetermined exhaust pressure receives assembly even in the absence of conventional tube sockets. u a .the proper amount of cooling air to .maintainthe tubes W111 noted the}? h cmfmt board together 1 at a temperature which will insure reliable Operation with the tubes and their sh1elds 1s separable from block To. review, the cooling air, after passing over the circuit and-consequently m Order 9 Pmveqt from leak board'14, flows over the tube leads, through the passages mg a h the F end of shleld annular pot controlled area between the tubes and theinrespective Surround-mg F shleld gasket, Provlded around shields, through the metering orifices, and then into the F t ohficesrsh duct' Exhaust chamber, or duct fo d by plate-S 26 andla The elimination of the tube sockets allows cooling air 2 It is.emphasized. that. the employment'of the foamed tovbevdrawn drrecflywover the tube leadS Wh1c h are ,plasticin the systemdoes not appreciably add to.-the TO Y' to h f some electrical ID51113- ..volurne-,or .weightofgan. electronic packageemploying m y he Tequh'ed' A5 111 the earher-descfihfid Y :.:c0nventional cooling techniques. By virtue of.-the.structhe cooling h P355687 C1086. t0 the tube ve ope to l plropertiesof th l ti th h i maybe d .Iefiect a high heattransfer coelficient, and the amountof of. -.much. Iightepgauge stock than isv necessary in con- -.air .supplied 10.621011 tube iS determined by thesizeof v-.ventiona],packaging.with theconsequence that the overall: 75.; the. orifice,-z.which,-, in. turn, is. proportional. to-the heat dissipation of the tube. Parallel flow of cooling air is employed, the low temperature inlet air first passing over the low temperature components and then'distributed among the several tubes of the chassis in accordance with their requirements. After discharge through the insure their reliability. Capacitor temperatures were kept below 185 F., and electron tube base temperature at or below 300 F. and hot spot temperatures were kept at or below 330 F. From the foregoing, then, it will be apparent that the packaging and cooling method combines the reliability of the electronic equipment with cooling air economy and allows the electronic designer complete freedom in the placement of components.

From the foregoing description of the systems of Figs. 1 and6, it will be apparent that they are applicable to the situation where the chassis is located in an ambient of sufiiciently low temperature that the ambient air can be used for cooling purposes; This situation is schematically represented in Fig. 8, which will serve to summarize the detailed description presented above and form a basis of comparison with other ambient conditions. In Fig. 8, the electronic package 100 is shown as a rectangular chamber having components of low heat density, which would include resistors and capacitors, grouped together in one area 102, and components of high heat density, such as vacuum tubes, grouped together in another area 104, spaced from area 102. The package 100 is located in an ambient of relatively low temperature, e.g., 50 F., a condition which mightprevail in an air-conditioned cabin of an aircraft. This air is suitable as a coolant, and may be drawn through the package in the direction indicated by the arrows to first pass over the components with low heat density, and then over the components of high heat density, with parallel distribution, and exhausted, say at 250 F. In order not to heat the air in the cabin, the exhaust air is discharged into a reservoir external of the cabin, preferably overboard. In accordance with the previous description, the hot components are thermally insulated from each other and from the components with low heat density by a mass thermal insulation, indicated at 106, to prevent the transfer of heat from the former to the latter. The

hot components are also thermally insulated from the ambient by thermal insulation indicated at.108 to prevent transfer of heat therefrom to the ambient, but the components in'area 102, since their operating temperature is not appreciably above that of the ambient, need not be thermally insulated from the ambient.

As shown in Fig. 9, the requirements for thermal insulation are reversed when the package-is located in an ambient having a temperature comparable to that of the exhaust air; e.g., 260 F. where an exhaust temperature of 250 F. affords reliable cooling. 'In this situation, ambient air obviously cannot be used as the coolant, it being necessary to supply air from an external source 110, which may be an air-conditioner delivering air at 50 F. As in Fig. 8, the hot components are insulated from each other,, -and from the components with low heat density by insulation 106, the cooling air passing over the components to .cool the same and thereafter exhausted, say at 250 F. [The ambient being at approximately the same temperature, it'.

is immaterial whether the heated air is exhausted to an external reservoir or to the ambient, and inasmuch as the ambient temperature is lower than the safe operating temperature of the hot components, thermal insulation between the hot components and the ambient will not congtn'biite to the cooling efficiency. The ambient tenipe fa ture, however, exceeds the safe operating temperature of ceeds the safe operating temperature of the hot components, for example, an ambient of 800 R, which might occur in a furnace or near the skin of a supersonic aircraft, the entire package must be thermally insulated from the ambient, as by a'thick covering of thermal insulation 114. As before, area 102 is thermally insulated from area 104, and cooling air drawn through the package from an external supply 110, for exhaust say at 250 5., into either an external reservoir or the ambient.

To summarize, in eachof the systems of Figs. 8, 9 and 10, the components with low heat density are thermally insulated from the components with high heat density, and the latter from each other, and cooling air of suitably low temperature drawn through the package in the direction of ascending temperature, parallel flow being employed to preferentially cool the hot components. If the ambient temperature is approximately equal to the inlet temperature of the coolant, the hot components only need be surrounded with thermal insulation; if the ambient temperature is approximately equal to the exhaust tem- -perature of the coolant, only the components with low heat density need be surrounded with thermal insulation;

and if the ambient temperature greatly exceeds the exhaust temperature of the coolant, both groups of components must be thermally insulated from the ambient.

Although the invention has been described as having particular applicability in the cooling of airborne electronic equipment, it is equally useful in other high temperature environments where the availability of cooling air is at a premium. For example, the system might be employed in the packaging of well-logging equipment,

- high temperatures being encountered in deep wells and the problem of supplying cooling air very diflicult, or in the packaging and cooling of electronic equipment installed in deep mines. Also, the system may be used to cool electronic equipment mounted near, or conceivably within a furnace, where it is necessary to thermally insulate the electronic parts from the ambient.

While particular embodiments of the invention have been shown, it is to be understood that applicants do not wish to be limited thereto since many modifications can now be made by ones skilled in the art, and applicants,

' therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of their invention.

What is claimed is: -1. An electronic equipment package comprising, in

combination, support means for electronic components,

electronic components with low heat density assembled in a first area "on said support means, electronic components with high heat densityassembled in a second area on said support means and spaced from said first area, a mass of thermal insulation formed with a plurality of recesses for receiving and surounding individual ones of the components in said second area for thermally insulating the same from the components in said first area and from each other,- means within each of said recesses defining passages for air directly in contact with each of said components with high heat density and communicating at one end with said firstarea, a duct communicating with the other end of each of said passages, said passages and a duct providing a path for the flow of cooling air through a said package in a direction from said first area toward said second area and through said passages into said duct, and thermal insulation separating at least one of said areas from the ambient surrounding said package.

2. An electronic equipment package comprising, in combination, a fiat circuit board, electronic circuit components with low heat density assembled in a group on a and surrounding individual ones of said components with:-

high heat density to thermally separate thesame from the components on said firstarea and from each other njieans in each of said recesses defining a passage. for air-- around :each of said components with high heat density, eachcommunicating at one end with; said first area, a; duct com :10

municating with each of said passages at the otherend ..thereof, and further thermal insulation arranged to..thermally separate the components in at least one'ofsaid areas from the ambient surrounding said package.

12 vAn.1 c tnl cttuipm pa agecompr si i -.cc rtbina i t block t s l suppo t s l -Wei 1= foamed, plastic material formed with a plurality'of cylindricaljlrecesses and a .duct communicating with each of 5 said:recesses,. andanelectronic chassis separably joined .7 to, said biOCkyfiiJd. including a circuit board having at ,-'lea st;-.resistorsand capacitorsmounted thereon and a plurality. of electron tubes extendingtherefrorn'and arranged ,to be substantially totallyenclosed within said recesses.

9... -An electronic equipment package comprising, in .-co rnbination, a ,block, of-self-supporting, lightrweight foamed plastic thermal insulating material formed with aplurality, of. cylindrical recessesand a duct communieating with .theinnerend of each of said recesses, acir- 3. The apparatus of claim 2; whe'rein said duct eqmrnnnh 15., cuitb ardhaving t l t r i crs n capacitors secur cates with said other, end of said passages through orifices of a size proportioned in accordance with; thecooling ,requirernents. of individual ones of said I components-with high. heat density.

.Hthereto, and a plurality of electron tubes extending from @anedge of Said board and lying in thepiane of said board, a,cylinmical shield surrounding each of said tubes and t, defining L llv annular passage between the tube and shield,

4. An electronicequipment package comprising, boom- 1'20 msaid ircuit board beingseparably joined to said block .bination, an electronic chassis including a circuit board having resistors and, capacitors assembled ina groupthere- ,on and a plurality of electron-tubes, assembled; -the re on with the leadsgof all directed toward said gronp ot rewith said tubflsand 'their respectivegshiclds inserted in l said cylindrical recesses.

Ihe apparatus of claim 9 wherein said. duct is ,7 internal: of said block and enclosed by thermal insulating isistors and capacitors and the axes of said tubes disppseda-lo material and communicates with said recesses through I substantially parallel to each other, a mass of foam-inplace plastic formed with alike. plurality: of; recesses each arranged to receive and enclose an individual one ofsaid tubes forthermally insulatingsaid tubeswfrom said red sisters and capacitors, from each; other; :-and;=fron1; the,

ambient surrounding the .package, means in cach of :said recesses defining an annular passage-for, airbet-ween each tube and said foam-in+plaee plastic,a ductriormed in said .t mass of plasticand communicating withv all'of said :pas-

: sages at a common end thereofland means :for drawing-r1 cooling air through saidpackage in .adirectionfrom said qresistors toward said duct, whereby the coolingair flows over ,said'resistors and capacitors, ,the ,tube leads, and the tubes in that order.

5. The apparatus of claim 4 wherein said duet communia-Q g cates with said passagethroughorifices proportioned to distribute the cooling airarnong said tubes in accordance with the heat dissipation and cooling requirements of the individual tubes.

6. An electronic equipment; package comprising, H1145 I; a like plurality of orifices having sizes related to the heat dissipation and cooiingrequirements of individualones o s idlt b llg An" electronic. equipment package comprising, in combination, anelectronic chassis including a flat circuit board having a first class, of components which mustbe operated at relatively low tcrnperatures and which dissipate arelativelysmall amount of heat in operation assembled in a group on at least one of the fiat surfaces of said board, and a second class of components which dissipate heat during operation and which may be reliably I operated at higher temperatures than said first ClaSSfOf components assembled in a groupv along one edge of said .board and extending therefrom substantially in theplane of said board, a mass of thermal insulation formed with 'a plurality of recesses arranged each to receive and enclose an'individual one of the components of said second class whereby the components of said second classare thermally insulated each from the other and from the components of, said first 61858, 11'133115 within each of said recesses defining an annular passage adjacent each of -the components of said second ciass, and a duct: communicating with each of said passages through orifices of a size proportioned in accordance with the heat dissi- .Side 311161601 ipfifpefldiclllfif i0 :board W thth ir- 'pation and cooling requirements of the individual comleads extending through corresponding; opens ofsaid openings, a cylindrical shield for eachof said tubes secured to said other side ofsaid board in register with said :openings and providing an; annular passage. 1for;;;air, in

ponents of said second class, said passages and'duct providing a path for the flow of cooling air through said passage in a direction to first pass over the components of said first classand through said passages in direct direct Contact With b H1855 f;:; he mal;in 5 contaee ith the components of said second class and :tion surrounding said shields andhaving ;a;duct-formed therein communicating with'each ofsaid passages, whereby cooling air drawnthroughsaid package in a -direction from said one side of said board toward said duct-cools the resistors andcapacitors, tube ;leads, .-tube ;base and,

, tube envelope, in that order. i

7. An electronicequipment;packagepgcomprising, 1n

combination, a block of self-supporting thermalinsulation formed withapplurality of'reccsseszanda duct intersecting each of said recesses,v an electronic: chassis in eluding .a circuit board having a likeplurality of electron tubes extending therefrom and arranged-within sa d re- 'cesses, a shield for. each ofsaid tubes definmg an annular passage around said.tube,;and an orificeplate-separatingeach Of saidpassages fromsaid duct.

into'said duct.

1 -.Reference's-ited inthe file ofthis patent .7 UNITED STATES PATENTS 

